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Salinity is one of the major constraints to crop production. Rice is a main staple food and is highly sensitive to salinity. This study aimed to elucidate the effects of salt stress on physiological and agronomic traits of rice genotypes with contrasting salt tolerance. Six contrasting rice genotypes (DJWJ, JFX, NSIC, HKN, XD2H and HHZ), including three salt-tolerant and three salt-sensitive rice genotypes, were grown under two different salt concentrations (0 and 100 mmol L−1 NaCl solution). The results showed that growth, physiological and yield-related traits of both salt-sensitive and salt-tolerant rice were significantly affected by salt stress. In general, plant height, tiller number, dry weight and relative growth rate showed 15.7%, 11.2%, 25.2% and 24.6% more reduction in salt-sensitive rice than in salt-tolerant rice, respectively. On the contrary, antioxidant enzyme activity (superoxide dismutase, peroxidase, catalase), osmotic adjustment substances (proline, soluble protein, malondialdehyde (MDA)) and Na+ content were significantly increased under salt stress, and the increase was far higher in salt-tolerant rice except for MDA. Furthermore, grain yield and yield components significantly decreased under salt stress. Overall, the salt-sensitive rice genotypes showed a 15.3% greater reduction in grain yield, 5.1% reduction in spikelets per panicle, 7.4% reduction in grain-filling percentage and 6.1% reduction in grain weight compared to salt-tolerant genotypes under salt stress. However, a modest gap showed a decline in panicles (22.2% vs. 22.8%) and total spikelets (45.4% vs. 42.1%) between salt-sensitive and salt-tolerant rice under salinity conditions. This study revealed that the yield advantage of salt-tolerant rice was partially caused by more biomass accumulation, growth rate, strong antioxidant capacity and osmotic adjustment ability under salt stress, which contributed to more spikelets per panicle, high grain-filling percentage and grain weight. The results of this study could be helpful in understanding the physiological mechanism of contrasting rice genotypes' responses to salt stress and to the breeding of salt-tolerant rice. [ABSTRACT FROM AUTHOR]

Background and objectives: The past four decades have seen a dramatic increase in cropping area of japonica inbred rice after the 1980s and nowadays occupies 90% of the total cropping area in Jiangsu, east China. To date, little attention has been paid to the effects of genetic improvements of japonica inbred rice on grain yield and grain quality under different nitrogen (N) levels. Fifteen japonica inbred rice released from 1983 to 2014 were investigated to evaluate changes in grain yield and grain quality of japonica inbred rice under 180 kg N/ha (N180), 270 kg N/ha (N270), and 360 kg N/ha (N360) during genetic progress. Findings: Genetic improvement increased (p <.01) rice grain yield and annual gain was 47.1, 60.2, and 75.6 kg/ha under N180, N270, and N360, respectively. During genetic progress, milling quality (milled rice percentage and head rice percentage), appearance quality (chalky rice percentage, chalky degree, and grain length‐to‐width ratio), and cooking and eating quality (gel consistency, overall palatability, breakdown, and setback) have been improved, while nutritional quality has been declined because of a reducing trend of protein content. Generally, the application of N fertilizer improved nutritional quality but deteriorated milling quality, appearance quality, and cooking and eating quality. Higher N application increased grain protein content, gel consistency, and breakdown, while decreased setback, which resulted in poor overall palatability. Conclusions: The results suggested great improvements in both grain yield and grain quality (especially milling, appearance, and cooking and eating qualities) of japonica inbred rice since the 1980s in east China. Modern rice cultivars respond more favorably to increased N application in terms of grain yield. N application improved nutritional quality but downgrades other quality traits. Significance and novelty: Our results proved a great success in breeding high‐yielding and good‐quality japonica inbred rice in east China since the 1980s. Future rice breeding for higher grain yield and better grain quality should rely both on improvements of breeding selection and cultivation practices, particularly concerning N management strategies. [ABSTRACT FROM AUTHOR]

Knowledge of changes associated with the progression of growth‐related characteristics in rice plant is essential to make strategies for future breeding and crop management. However, thus far, little attention has been given to the identification of temporal changes of the traits concomitant with the year of release in rice genetic breeding. The objective of this study was to explore genetic gain for yield accrued in association with evolution of the growth phenotypes in a 2‐year field experiment conducted on the Yangtze River Basin of China. Fifteen rice (Oryza sativa L.) cultivars, including 5 super high‐yielding rice, bred or widely cultivated from 1936 to 2005, were grown in irrigated field conditions with appropriate doses of commercial fertilizers during the rice‐growing season from May to October in 2013 and 2014. In both years, SPAD reading was high during vegetative and early grain filling stages, but it declined sharply at maturity. In general, SPAD reading increased with the progression in year of release of the cultivars and it correlated with yield benefit accrued. Similar to SPAD, the evolutionary trend also accounted for significant increases in LAI (leaf area index) and SLW (specific leaf weight), CGR (crop growth rate), LAD (leaf area duration), S/LA (spikelets/leaf area), and NAR (net assimilation rate). All growth parameters, except NAR, correlated positively with grain yield. Conversely, K (extinction coefficient) exhibited significant decline along with year of release, meaning more erect canopies. Gain of SLW in the newer cultivars enabled better light energy interception probably with higher RUE, which associated with increased SPAD amounting to low K values. It was opined that the reduced K improved light distribution across the leaves, which contributed to a grain yield advantage through increase of sink size (S/LA) over the 70‐year period. [ABSTRACT FROM AUTHOR]

Since genetic improvement greatly promoted an increased yield japonica inbred rice in east China after the 1990s, better root characteristics were certainly expected. In 2018 and 2019, nine japonica inbred rice released in the 1990s, 2000s, and 2010s were investigated to evaluate the changes in root morpho-physiology and identify root traits that contributed to the positive yield trends during the genetic process. The 2010's rice had 8.0 and 4.3% higher grain yield than the 1990's and the 2000's rice, respectively (p < 0.05). Genetic yield gain was mainly attributed to the increased spikelets per panicle. Compared with the 1990's and the 2000's rice, the 2010's rice had higher shoot biomass at heading and maturity (p < 0.05), as well as root biomass (p < 0.05), especially for root biomass of 15–30 cm soil depth. Leaf area index (LAI), soil-plant analysis development (SPAD) values, and leaf photosynthetic rate at middle grain-filling period (MGP) and late grain-filling period (LGP) were all increased. The 2010's rice had consistently higher root length and volume, root oxidation activity, and root bleeding rate at MGP and LGP than the 1990's and the 2000's rice (p < 0.05). Positive correlations were detected between root length and volume, root oxidation activity, and root bleeding rate at MGP, LGP, and SPAD values, leaf photosynthetic rate at MGP and LGP, and higher shoot biomass accumulation after heading and grain yield (p < 0.05 or p < 0.01). The present study implied that genetic improvement optimized post-heading root morphology and physiology, which maintained shoot stay-green and facilitated biomass accumulation and yield increase in japonica inbred rice during the genetic process since the 1990s. [ABSTRACT FROM AUTHOR]

The past three decades have seen a pronounced development of conventional japonica rice from the 1990s, although little information is available on changes regarding grain yield and nutrient use efficiency during this process. Nine conventional japonica rice released during the 1990s, 2000s, and 2010s were grown under a reduced nitrogen rate, with increased planting density (RNID) and local cultivation practice (LCP) in 2017 and 2018. The rice from the 2010s had 3.6–5.5% and 7.0–10.1% higher (p < 0.05) grain yield than the 2000s and the 1990s, respectively, under RNID and LCP. The harvest index contributed more to genetic yield gain from the 1990s to the 2000s; whereas from the 2000s to 2010s, yield increase contributed through shoot biomass. Genetic improvement increased total nitrogen (N), phosphorus (P), and potassium (K) accumulation, and their use efficiencies. The rice from the 2010s showed a similar grain yield, whereas the 1990s and 2000s' rice exhibited a lower (p < 0.05) grain yield under RNID relative to LCP. RNID increased N, P, and K use efficiencies, particularly the N use efficiency for the grain yield (NUEg) of the 2010s' rice, compared with LCP. For three varietal types, RNID increased the panicles per m2, the filled-grain percentage, and the grain weight (p < 0.05) while decreasing spikelets per panicle of the 2010s' rice. Compared with LCP, RNID reduced non-structural carbohydrate (NSC) content and shoot biomass, at heading and maturity, while increasing the remobilization of NSC and the harvest index, especially for the 2010s' rice. Our results suggested the impressive progressive increase in grain yield and nutrient use efficiency of conventional japonica rice since the 1990s in east China. RNID could facilitate grain yield and NUEg for modern conventional japonica rice. [ABSTRACT FROM AUTHOR]

Grain yield was greatly increased during the genetic improvement of japonica inbred rice since the 1980s in Jiangsu, east China; thus, an improved plant morphology should be expected, considering that plant morphology is a decisive factor determining grain yield. Twelve representative japonica inbred rice released from 1983 to 2013 were grown in the same fields in 2019 and 2020. Grain yield increased (p < 0.01) at 63.3 kg ha−1 year−1 across 2 years among rice cultivars released in different periods. The genetic improvement in grain yield was associated with increased spikelets per panicle. Single panicle weight, number of primary and secondary branches, and number of grains on primary and secondary branches were all increased with a year of release. Generally, the width of top three leaves positively correlated (while angle of top three leaves and light extinction coefficient negatively) correlated (p < 0.01) with year of release. Leaf area per tiller and leaf area index at heading and maturity, specific leaf weight, leaf photosynthetic rate, and SPAD values after heading were all increased linearly with year of release. Plant height exhibited a positive (p < 0.01) trend with year of release, as well as stem weight per tiller and K and Si concentrations of stem. Spikelets per panicle, width of top three leaves, plant height, and leaf area index, and specific leaf weight after heading positively correlated (while angle of top three leaves and light extinction coefficient negatively) correlated (p < 0.01) with grain yield and single panicle weight. Our results suggested that modern japonica inbred rice exhibited expanded sink size by spikelets per panicle, higher leaf area through leaf width, optimized leaf photosynthetic capacity, lower leaf angle and light extinction coefficient, and enhanced stem strength. These improved plant morphologies facilitated yield increases of japonica inbred rice since the 1980s in east China. [ABSTRACT FROM AUTHOR]

Because of inadequate water resources and poor irrigation facilities, salinity and drought stresses often co-occur in rice production in saline lands. Nevertheless, little information is available on the agro-physiological traits and grain yield of rice when subjected to combined salinity × drought stress. We evaluated the individual and interactive influences of salinity and drought on rice yield and agro-physiological characteristics using two rice cultivars, Nanjing 9108 (salinity-tolerant rice) and Wuyunjing 30 (salinity-susceptible rice). This experiment was conducted under non-salinity (NS) and salinity (S) conditions and three drought levels from jointing to heading (CC, control condition; MD, moderate drought; SD, severe drought). Individual salinity and drought treatments and their combination shortened the total growth duration by 3–4 days and 4–6 days in Nanjing 9108 and Wuyunjing 30, respectively. Both salinity and drought treatments reduced (P < 0.01 or P < 0.05) rice yield by 12.9%−40.9% and 28.1%−35.0% across the two cultivars, respectively, and the combined salinity × drought treatment resulted in a more pronounced yield loss of 53.1%−113.3%. A greater reduction in grain yield caused by the combined salinity × drought stress was detected in Wuyunjing 30 than in Nanjing 9108. The poor grain yield performance of rice under combined salinity × drought stress was mainly attributable to the following: (1) yield components, panicle length, and single panicle weight were lower than they were under an individual stress; (2) combined stress caused greater reductions in shoot biomass, leaf area index (LAI), and nonstructural carbohydrate (NSC) content in the stem at heading and maturity, although harvest index and NSC remobilization reserve were increased; (3) each stress and especially combined stress increased Na+/K+ ratio in the leaf, while reducing leaf photosynthetic rate and SPAD values after heading, and total accumulation of nitrogen (N), phosphorus (P), and potassium (K). Our results suggested that the combined salinity × drought stress was more damaging than either stress alone, and resulted in a greater yield penalty of rice. In terms of grain yield, salinity-susceptible rice was more responsive to the combined stress than salinity-tolerant rice. • The effects of combined salinity × drought stress on rice yield and NPK uptake were evaluated. • The combined salinity × drought stress reduced rice yield more than either stress alone. • Salinity-susceptible rice was more responsive to the combined salinity × drought stress. [ABSTRACT FROM AUTHOR]

The cropping area of japonica inbred rice has expanded rapidly since the 1980 s, which occupies 90% of the total cropping area nowadays in Jiangsu, east China. In this process, information on the genetic improvement in grain yield and nutrient use efficiency of japonica inbred rice is still limited. Fifteen japonica inbred rice released from 1983 to 2014 were tested during the 2018 and 2019 rice-growing seasons. Grain yield increased yearly at 65.1 kg ha−1 (0.65%) in 2018 and 58.1 kg ha−1 (0.59%) in 2019. Panicles per m2 and filled-kernel percentage decreased (P < 0.01), while spikelets per panicle increased (P < 0.01), with year of release. Pre-heading biomass, post-heading biomass, and total biomass increased (P < 0.01 or P < 0.05) linearly with year of release; while harvest index gradually increased with year of release before 2000, thereafter remaining relatively stable. Leaf area index (LAI) at heading and maturity, plant height, specific leaf weight, and flag leaf photosynthetic rate at heading, and intercepted radiation and radiation use efficiency (RUE) from heading to maturity all increased (P < 0.01) with year of release, which was associated with the increased biomass accumulation during the breeding process. Genetic improvement has increased total N, P, and K accumulation, as well as their use efficiencies. Grain yield and harvest index correlated positively (P < 0.01) with NUEg, PUEg, and KUEg among rice cultivars. Our results suggested the impressive progress in grain yield and nutrient use efficiency of japonica inbred rice since the 1980 s in eastern China. The yield progress was mainly attributed to the increased spikelets per panicle. For rice cultivars released before 2000, an increase in harvest index contributed more to yield improvement than total biomass; while the yield improvement after 2000 resulted from total biomass. The results also indicated possible opportunities for improving use efficiency of N, P, and K through increasing harvest index in rice. • Genetic improvement has progressively increased grain yield of japonica inbred rice since the 1980s in eastern China. • The increased harvest index contributed more to yield gain before 2000, while total biomass for yield gain after 2000. • Genetic selection for rice grain yield has also improved N, P, and K use efficiencies. • Harvest index was positively (P<0.01) correlated with NUEg, PUEg, and KUEg in rice. [ABSTRACT FROM AUTHOR]

• JIH exhibited yield superiority over IH not only in non-saline fields, but also in saline fields. • Limited shoot and root growth were responsible for the yield penalty of rice under saline field conditions. • The improved agronomic and physiological traits of JIH facilitated superior grain yield over IH in saline fields. It is of great interest to utilize saline fields to promote rice production in China. Previous studies reported greater yield productivity of japonica/indica hybrids (JIH) over indica hybrids (IH) under nonsaline fields. It has still not been established how salinity stress intervenes with rice yield and whether JIH would exhibit superior grain yield than IH under saline field conditions. This study investigated three JIH and three IH cultivars grown at the two sites that differed significantly in soil salinity, namely, nonsaline (Wulie, abbreviated as WL) and saline (Tiaozini, abbreviated as TZN) fields, in Yancheng, Jiangsu, China. The panicles per m2, spikelets per panicle, filled-kernel percentage, and kernel weight of JIH and IH were reduced, and a 36.0 %–43.5 % loss in grain yield was observed with salinity stress at TZN compared with WL. For JIH and IH, the shoot biomass and leaf area index (LAI) at jointing, heading, and maturity were all reduced at TZN compared to those at WL; similar results were also detected for root biomass, root length and volume, and root bleeding rate after heading. Compared with IH, JIH produced a 24.8 % higher grain yield under saline field conditions at TZN across two years. Four agronomic and physiological traits were summarized for superior grain yield of JIH compared to that of IH with salinity stress under field conditions. First, JIH had an enlarged sink size potential of a greater number of spikelets per panicle. Second, a synergistically increased biomass accumulation and harvest index of JIH, supported by higher biomass accumulation and LAI at the main growth stages and improved NSC remobilization after heading. Third, JIH had an improved stay-green characteristic, indicated by a higher leaf area per plant, SPAD values, and leaf photosynthetic rate after heading. Fourth, JIH exhibited a better root morpho-physiology than that of IH after heading, showing a larger and deeper root structure and higher root bleeding rate. These results indicated that the limited shoot and root growth were responsible for the yield penalty of rice under saline field conditions. JIH's improved agronomic and physiological traits facilitated superior yield performance over IH with salinity stress under field conditions. [ABSTRACT FROM AUTHOR]